Image reconstruction architecture

ABSTRACT

Methods and apparatus for reconstructing digitized images are provided that include an image reconstruction path that receives a digitized image and provides a processed RGB or CMYK image that may be printed or stored in memory. The image reconstruction path is configured to operate in either a multiple scan or single scan environment if the source of the digitized image is a scanner. A plurality of optional functional units in the reconstruction path can be controlled by user or internal controls. These functional units perform preliminary color adjustment, automatic deskew, background and dust removal, descreen, text detection and enhancement, color conversion, scaling, and color manipulation.

REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. application Ser. No.09/314,573, filed May 18, 1999, now U.S. Patent No. ______.

FIELD OF THE INVENTION

[0002] The invention relates digitized image processing systems, and inparticular to image reconstruction architectures in which digitizedimages that are obtained from an image source, such as a scanner, areprocessed for output to an output device, such as a printer.

BACKGROUND

[0003] Image processing systems typically are used to adjust and correctimage signals. For example, when printing a digitized image, suchadjustments and corrections can include: color adjustment, deskewing,background and dust removal, descreening, text detection, textenhancement, color conversion, scaling and color manipulation.

[0004] In most image processing systems, digitized image signalcorrectors perform the adjustments or corrections based on processingparameters provided by a system operator. The task of selecting theappropriate processing parameters for these correctors to achievecertain desired output results is normally left to the operator, and isone of the more difficult tasks in image processing. As the complexityof the image processing model grows with advances in image processingtechnology, this task has become even more difficult.

[0005] For most adjustments or corrections, the operator typically doesnot want to know about the particular processing parameters being used,but instead wants to achieve the desired output results. Thus, it isdesirable to determine optimal processing parameters for digitized imagesignal correctors automatically to achieve specified output results foran image.

[0006] Examples of previously known automatic or semi-automatic imageprocessing systems include Spiegel et al. U.S. Pat. No. 5,615,282 andCapitant et al. U.S. Pat. No. 5,467,412. Such previously known systems,however, provide only limited image reconstruction capability. Forexample, such systems do not incorporate descreening or text detectionfacilities, and therefore an image reconstruction subsystem must beappended thereto. Further, such systems do not provide multiple datapaths (e.g., for single and multiple scans) and do not support bothcontone and 1-bit printing.

[0007] It would be advantageous to provide improved methods andapparatus for reconstructing digitized images.

SUMMARY

[0008] The invention provides improved methods and apparatus forreconstructing digitized images. The invention processes one or morecolor formats (e.g., contone or 1-bit), and readily operates with imagesources that can include both single and multiple scan systems. Forpurpose of the discussion herein, multiple scan refers to systems thatscan an image once per print separation. That is, for a CMYK printingsystem, the image is scanned four times, and printing separations for C,M, Y, and K are generated one by one. In contrast, single scan refers tocopy systems that scan an image once for all print separations. Thus,for a CYMK printing system, the image is scanned once.

[0009] An exemplary embodiment of the invention provides an imagereconstruction path that receives a digitized image, for example, from ascanner or memory, and provides a processed RGB or CMYK image that maybe printed or stored in memory. The image reconstruction path isconfigured to operate in either a multiple scan or single scanenvironment when the source of the digitized image is a scanner. Withinthe image reconstruction path, there are a plurality of functional unitsthat can be controlled by user or internal controls, or that can beoptionally bypassed. These functional units provide any of preliminarycolor adjustment, automatic deskew, background and dust removal,descreen, text detection and enhancement, color conversion, scaling, andcolor manipulation. It will be appreciated by those skilled in the artthat other functions also may be provided.

[0010] An important feature of this architecture is that it isopen-ended on both the input and output ends. This means that with theappropriate customization, the architecture is ready to accommodatedifferent scanners at the input source and different printers at theoutput target.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The above-mentioned objects and features of the present inventioncan be more clearly understood from the following detailed descriptionconsidered in conjunction with the following drawings, in which the samereference numerals denote the same elements throughout, and in which:

[0012]FIG. 1 is a block diagram of a digitized image processing systemincluding an exemplary image reconstruction path in accordance with thisinvention;

[0013]FIGS. 2a and 2 b provide a processing flow diagram for anexemplary image reconstruction path that processes a multipass scannedimage in accordance with this invention; and

[0014]FIGS. 3a and 3 b provide a processing flow diagram for anexemplary image reconstruction path within a single scan system inaccordance with this invention.

DETAILED DESCRIPTION

[0015] The invention provides improved methods and apparatus forreconstructing digitized images. One important feature of the inventionincludes the ability to process one or more color formats, e.g., contoneor 1-bit, and to operate upon any image source. For purpose of thediscussion herein, multiple scan refers to systems that scan an imageonce per print separation. That is, for a CMYK printing system, theimage is scanned four times, and printing separations for C, M, Y, and Kare generated one by one. In contrast, single scan refers to copysystems that scan an image once for all print separations. For example,for a CYMK printing system the image is scanned once.

[0016] Referring to FIG. 1, a digitized image processing systemincluding an exemplary image reconstruction path in accordance with thisinvention is described. Image reconstruction path 10 accepts digitizedimage data from any of several sources, such as memory 14, video 12(including data that may be cropped 13 or otherwise processed) JPEG orother image data 16 (such as GIF, TIFF, or PICT data), and RGB data 18(e.g., from a scanner). In the case of video data, the system provides amechanism, as is known in the art, for decompressing and deblocking thedata, upsampling, and converting YUV to RGB 19.

[0017] Image reconstruction path 10 provides a front end capability forprocessing any type of digitized image data, although the internaloperation of the image reconstruction path is based upon the ultimatereceipt of digitized image data in an RGB format. Persons of ordinaryskill in the art will understand that image reconstruction paths inaccordance with this invention may be configured to operate on digitizedimage data in any format, and that the exemplary embodiment of theinvention is provided solely for purposes of illustration and exampleand is not intended to limit the scope of the invention in any way.

[0018] Image reconstruction path 10 is for a single scan system.Referring to FIG. 2, an appropriate image reconstruction path for amultipass architecture is now described. In the image reconstructionpath, each functional unit can be controlled by either of a user or byinternal controls. Additionally, inclusion of each of the functionalunits in the image reconstruction path is optional. The system has asits default an automatic behavior which can be suppressed by theoperator, either by turning some automatic functions ON or OFF, or bycontrolling the parameter settings for those functions. Accordingly, theapparatus and methods in accordance with this invention provide theflexibility to include only those functional units of interest to theuser. In an exemplary embodiment of the invention, the user may selectthe desired functional units from a selection menu, such that the imagereconstruction path is readily reconfigured for each job.

[0019] Functional units within the image reconstruction path may includeany of:

[0020] Image rotation, duplexing, and tiling.

[0021] Preliminary color adjustment: this functional unit converts theword size of the input image data as desired, and thereby stretches theinput data to a desirable dynamic range. For example, the preliminarycolor adjustment functional unit receives images data from the scannerat 8-12 bits per component and returns 8-bit adjusted RGB values throughthe use of one-dimensional curves. This is done by using a look-up-table(LUT) sized by the number of possible input combinations, e.g. 4096entries for 12 bit input.

[0022] Automatic deskew: this functional unit performs small anglecorrections for originals that are misplaced on the scanner's glassduring the scanning process. Such techniques are well known in the art.

[0023] Background and dust removal: this functional unit removes noise,dust, and uniform background, as requested by the user. Such techniquesare well known in the art.

[0024] Halftone detection: this functional unit detects areas of theimage that were originally printed using a halftoning process, i.e.,screen or error diffusion. One such halftone detection process isdescribed in Karidi U.S. Pat. No. 6,185,335, which may be used toperform the function of this functional unit. The descreening algorithmdisclosed therein preserves soft edges. Therefore, a preferred approachto halftone detection in the exemplary embodiment of the invention marksall possible screen areas for descreening unless sharp edge informationis lost thereby, e.g., boundaries of graphics and characters. Inexemplary embodiments of the invention, the halftone detection procedureis applied to the intensity component Y of the image. For each pixel, adecision is made whether the pixel is dark or light relative to itsneighborhood (e.g., a 5×5 neighborhood). Each pixel is then consideredwith a surrounding window (e.g., a 9×9 surrounding window) and the sizeof the boundary set between the dark and light classes is measured. Apixel is marked as a halftone candidate only if the boundary size isless than a probabilistic estimate.

[0025] Descreen: this functional unit reconstructs a contone image fromhalftone data obtained during the halftone detection procedure describedabove. An exemplary descreening process is described in Karidi U.S. Pat.No. 6,222,641, which may be used to perform the function of thisfunctional unit. In this procedure, an adaptive, edge-preserving lowpass filter is applied to areas that are marked as halftone. For eachpixel that is marked as halftone, a descreening kernel is applied toproduce a smoothed neighborhood of the pixel. Within this smoothcontext, locations of those pixels whose values are within a certainthreshold of the current pixel are marked. These locations are used tobuild a 0-1 mask that is applied to the low pass filter kernel. Themasked kernel is then convolved with the original, i.e. non-smoothed,neighborhood of the current pixel. To avoid over-smoothing, the originalpixel value is restored if the variation within the original window issmaller than one threshold, or the number of marked pixels is smallerthan another threshold.

[0026] Text detection: this functional unit decides which parts of theimage contain text. In exemplary embodiments of this invention, textcomprises black text on a white background, although other textdetection schemes may be used. An exemplary text detection process isdescribed in Karidi U.S. Pat. No. 6,289,122, which may be used toperform the function of this functional unit.

[0027] Text enhancement: this functional unit makes the text clear andsharp. Exemplary embodiments of this invention only enhance black texton a white background. An exemplary text enhancement process isdescribed in Karidi U.S. Pat. No. 6,185,335, which may be used toperform the function of this functional unit. In this exemplaryembodiment of the invention, the ink component is processed. Todetermine the ink level, e.g., 0-255, where 0=white, from the intensitylevel, a one dimensional look up table (LUT) is applied. After resealingto the printing resolution, the total amount T of ink is a surroundingwindow (e.g., a 5×5 window) is measured. The number of pixels C that aredarker than the current pixel are counted. In simplified form, adetermination is made as follows: if (T>255× dot factor x C), then putink in the current pixel; otherwise leave the pixel white. Textenhancement is preferably customized in 1-Bit systems, but need not incontone systems.

[0028] Color conversion: this functional unit converts from scannercolor space to the printer/host color space. In an exemplary embodimentof the invention, the procedure interpolates a color table from theinput color space (i.e. RGB) to the output color space (e.g. RGB orCMYK). The interpolation is either linear (i.e., tetrahedral) ormulti-linear. The color table is a composition of the scannercalibration table (e.g., from scanner RGB to a standardized orproprietary RGB used by the image reconstruction path) and the printingengine's Color Rendering Dictionary (CRD). The inputs to this functionalunit include text detection tags to ensure that black text is printedwith black ink only. For pixels that were marked as text, a threedimensional table is not typically used. Rather, a separate, Y to K, onedimensional table is used.

[0029] Scale: this functional unit selects the image up/down to mapprint resolution and the user input. The exemplary embodiment of theinvention uses bi-cubic interpolation. Interpolation for scaling is awell known technique.

[0030] Color manipulation: this function unit supports brightness, colorsaturation, and contrast adjustments. These functions are implementedthrough LUT's and linear operations (e.g. matrix multiplication).

[0031] After the image data have been processed via the imagereconstruction path, the processed data are provided to an output module20 that formats the image data as RGB/CMYK data, as appropriate for theoutput device. For example, the output device may be a computer memory22, in which case the data may be maintained in an RGB format and/orcompressed via a compression module 21. If the image data are to beprovided to a printed by a printer 23, then the data are formatted asCMY or CMKY data for use by the printer.

[0032]FIGS. 2a and 2 b provide a processing flow diagram for an imagereconstruction path that correspond to a multi-scan system in accordancewith this invention. Thus, the processing flow shown on FIGS. 2a and 2 bis traversed four times for a CMYK printer, once for each of the fourseparations. During an image scan, an input signal 30 is provided to theimage reconstruction path. Preliminary color adjustment is performed 31,resulting in an R′,G′,B′ and a Y′ signal output 32. The imagereconstruction path performs a preliminary tagging operation 33 toproduce preliminary color tags 34.

[0033] The color conversion procedure 35 is next applied, resulting in acurrent color signal (CC) and an intensity signal (Y) 36. No use of R′,G′, B′ or Y′ information is made from this point on 37 in the imagereconstruction path because processing now proceeds for a current colorchannel in the multi-scan cycle.

[0034] The current color and intensity information, along with thepreliminary tags, is provided to the dust and background removalfunction 38, resulting in a clean current color signal, a cleanintensity signal, and classification tags 39. Classification tagscontain information related to color, e.g., an indication of how neutrala pixel is, whether a pixel is within an edge, or whether a pixel is ina high contrast region. The classification tags also record pixellocations for which background removal was applied.

[0035] The clean intensity signal is binarized for halftone detection40, resulting in a binarized intensity signal 41. The binarizedintensity signal is then applied to the halftone detection function 42to produce halftone tags 43.

[0036] The clean current color information is smoothed for descreening44, resulting in smoothed current color information 45. The cleancurrent color information, smoothed current color information, andhalftone tags are applied to the descreening functional unit 46,resulting in descreened Current Color and intensity information andhalftone tags 47.

[0037] The descreened intensity information and the classification tagsare then applied to the text detection functional unit 48, resulting intext tags 49. The text tags and scaled intensity information areprovided to the text enhancement functional unit 50, resulting inenhanced text and intensity information 51.

[0038] The scaled current color, intensity value of the enhanced text,and text tags are applied to a merge text function 52, resulting inreconstructed current color and intensity information. The reconstructedcurrent color and intensity information is applied to the scalefunctional unit 54, resulting in scaled current color and intensityinformation 55. The scaled current color and intensity information isapplied to a halftone threshold array or error diffusion functional unit57. Typically, a 1-bit system requires an error diffusion based halftonemodule, while a contone system requires a threshold array based halftonesystem. Thereafter, an output is provided 56 to the selecteddestination, e.g. printer or memory.

[0039] Referring now to FIGS. 3a and 3 b, a processing flow diagram isdescribed for an image reconstruction path in a single scan system inaccordance with this invention. During a scan of an image by thescanner, an input RGB signal 150 is provided to the image reconstructionpath. Preliminary color adjustment is performed 151, resulting in anR′,G′,B′ and a Y′ signal output 152.

[0040] The R′,G′,B′ and Y′ information is provided to the dust andbackground removal function 153, resulting in clean R,G,B and Y signalsand class tags 154. The clean intensity signal is binarized for halftonedetection 155, resulting in a binarized intensity signal 156. Thebinarized intensity signal is then applied to the halftone detectionfunction 157 to produce halftone tags 158.

[0041] The clean RGB information is smoothed for descreening 159,resulting in smoothed RGB information 160. The clean RGB information,smoothed RGB information, and halftone tags are applied to thedescreening functional unit 161, resulting in descreened R,G,B andintensity information, halftone tags, and neutral tags 162. Neutral tagsare similar to classification tags and indicate whether a pixel isneutral or colored.

[0042] The descreened intensity information, class tags, halftone tags,and neutral tags are then applied to the text detection functional unit163, resulting in text tags 164. The text tags and scaled intensityinformation are provided to the text enhancement functional unit 165,resulting in enhanced text and intensity information 166.

[0043] The RGB, intensity value of the enhanced text, and text tags areapplied to a color conversion function 167, resulting in either of RGBor CMYK information 168. The reconstructed RGB or CMYK information isapplied to the scale functional unit 169, resulting in scaled RGB andintensity information 170. There is no need to write this information tomemory 171.

[0044] The RGB/CMYK information is applied to a halftone threshold arrayor error diffusion functional unit 172. Typically, a 1-bit systemrequires an error diffusion based halftone module, while a contonesystem requires a threshold array based halftone system. Thereafter, anoutput RGB/CMYK and text K layer signal is provided 173 to the selecteddestination, e.g. printer or memory.

[0045] The foregoing merely illustrates the principles of thisinvention, and various modifications can be made by persons of ordinaryskill in the art without departing from the scope and spirit of thisinvention.

I claim:
 1. A method for reconstructing a digitized image provided by ascanner or an image memory, the method comprising: providing thedigitized image to an image reconstruction path that is capable orproducing RGB and CMYK output images; and providing the output images toany of a printer or an image memory.
 2. The method of claim 1, whereinthe digitized image comprises an image that is stored in any knownformat.
 3. The method of claim 1, wherein the digitized image comprisesany of video, image, and RGB data.
 4. A method for reconstructing adigitized image provided by a scanner or an image memory, the methodcomprising: providing the digitized image to an image reconstructionpath that is selectively configurable to process images produced bysingle scan and multiple scan copy systems; and providing the outputimages to any of a printer or an image memory.
 5. The method of claim 4,wherein the digitized image comprises an image that is stored in anyknown format.
 6. The method of claim 4, wherein the digitized imagecomprises any of video, image, and RGB data.
 7. A method forreconstructing a digitized image provided by a scanner or an imagememory, the method comprising: providing the digitized image to an imagereconstruction path that is selectively configurable to process imagesfor reproduction on 1-bit and contone printing devices; and providingthe output images to any of a printer or an image memory.
 8. The methodof claim 7, wherein the digitized image comprises an image that isstored in any known format.
 9. The method of claim 7, wherein thedigitized image comprises any of video, image, and RGB data. 10.Apparatus for reconstructing a digitized image provided by a scanner oran image memory, the apparatus comprising: means for providing thedigitized image to an image reconstruction path that is capable orproducing RGB and CMYK output images; and means for providing the outputimages to any of a printer or an image memory.
 11. The apparatus ofclaim 10, wherein the digitized image comprises an image that is storedin any known format.
 12. The apparatus of claim 10, wherein thedigitized image comprises any of video, image, and RGB data. 13.Apparatus for reconstructing a digitized image provided by a scanner oran image memory, the apparatus comprising: means for providing thedigitized image to an image reconstruction path that is selectivelyconfigurable to process images produced by single scan and multiple scancopy systems; and means for providing the output images to any of aprinter or an image memory.
 14. The apparatus of claim 13, wherein thedigitized image comprises an image that is stored in any known format.15. The apparatus of claim 13, wherein the digitized image comprises anyof video, image, and RGB data.
 16. Apparatus for reconstructing adigitized image provided by a scanner or an image memory, the apparatuscomprising: means for providing the digitized image to an imagereconstruction path that is selectively configurable to process imagesfor reproduction on 1-bit and contone printing devices; and means forproviding the output images to any of a printer or an image memory. 17.The apparatus of claim 16, wherein the digitized image comprises animage that is stored in any known format.
 18. The apparatus of claim 16,wherein the digitized image comprises any of video, image, and RGB data.